1. Field of Invention
The invention relates to systems and methods for providing a compensation factor for a registration system that takes into account differing physical characteristics of various substrates used in the system. In particular, a compensation factor, such as a theoretically or an empirically derived paper path length adjustment value, is stored for various substrates and used in drive roll control profile computations to provide process direction registration control of the substrates passing through the system.
2. Description of Related Art
There are a variety of transport and registration systems in use that transport and register various substrates, such as copy sheets. In many registration systems, such as those often found in copiers, facsimiles, and printers, drive mechanisms often include at least one driven elastomer-covered roll backed by a hard idler roll to form a roll pair defining a nip region therebetween. A substrate, such as copy paper, provided to the nip region is advanced by rotation of the roll pair, which causes corresponding linear movement of the substrate, such as paper.
High quality documents require registration of sheets to a photoreceptive surface for image transfer. In order to achieve this, accurate registration control is needed to locate the image with respect to the edge of the sheet. Conventional machines use various types of sheet registration devices. Some sense the position of the sheet at a first location and use this sensed information to generate a set of control signals to cause the sheet to arrive at a second location in proper registry. Other systems compute or approximate sheet position Indirectly based on known parameters of the registration system and sensed values of various drive elements.
In most conventional registration systems used for printers, copiers and facsimile machines, the types of substrates being transported usually do not vary much. That is, many systems typically encounter only a limited number of different substrate types, such as basic draft sheet stock of a certain weight in basic sizes such as A4 or 8.5×11 inches. A typical registration system is designed to transport, for example, 20 lb. bond sheet stock (roughly 75 grams/m2 or GSM). Occasionally, higher quality bond paper of a slightly higher weight, such as 24 lb. bond (roughly 90 GSM) or 28 lb. bond (roughly 105 GSM) sheet stock is used. In conventional registration systems, these sheets are transported using the same drive profiles. That is, the drive control parameters are fixed (i.e., set irregardless of the type of sheet being used).
In conventional drive roll systems, angular velocity and degrees of rotation of the driven roll can be readily determined from conventional measurement systems, such as rotary encoders. From this information and knowledge of the roll radius of the drive roll, the system can, through equations, approximate the linear movement of the substrate passing through the nip region. This linear movement, including travel velocity, is relevant because various timing and other position control is based on the determined linear velocity of the substrate. For example, if It is desired that a substrate reach a desired position such as a leading edge transfer position 1000 mm from the drive roll at a given time t, through computation knowing both the distance (1000 mm) and the determined linear velocity (X mm/sec), the time to start the transport can be calculated. Alternatively, or in addition thereto, a desired velocity can be set to match other system components so that the substrate is at a select location at a desired speed and at a desired time based on the determined linear velocity.